To attain a higher operation speed in a large electronic computer, it is necessary to attain a higher signal propagation speed in a semiconductor device itself and in a system in which the device is packaged. In recent years, for semiconductor devices, the development of high-integration technology has resulted in markedly higher speed and higher integration, and the packaging technology has come to affect greatly on increasing the operation speed. As to the packaging technology, ceramic multilayer circuit substrates have come to be used in order to enable a high density packaging of semiconductor devices and to reduce the delay of electric signals. Previously, alumina has been generally used as the insulating material for ceramic multilayer circuit substrates. In recent years, however, to enhance the properties of the substrate further, there have been studied and developed low-temperature sintered substrate materials, such as those described in "multilayer ceramic substrate" [Japanese Patent Application Kokoku (Post-Exam. Publn.) No. 22,399/84], and low-temperature sintered material of low dielectric constant formed by bonding silica with glass, such as those described in "ceramic multilayer wiring circuit board" [Japanese Patent Application Kokai (Laid-open) No. 11,700/84]. In these circuit board materials, which are obtained by sintering the original material densely so as to contain as few pores as possible therein, the specific dielectric constant, which affects greatly on attaining a higher operation speed, is about 4 to 5 at the lowest.
Further, there have been already obtained, for the purpose of heat insulation, weight reduction, or sound insulation, substrates which contain pores within the ceramics, such as those described in "composite ceramic electronic material" [Japanese Patent Application Kokai (Laid-open) No. 89,212/82] and "process for producing foamed ceramic board" [Japanese Patent Application Kokai (Laid-open) No. 83,985/84]. However, no consideration has been given to these substrates for using them as the substrate material for large electronic computers in which a higher signal propagation speed is required.
On the other hand, with the advent of semiconductors of higher speed and higher density, methods have come to be used in which semiconductor devices are directly packaged on a ceramic multilayer circuit substrate in order to facilitate heat radiation and to increase the speed of the device. However, this packaging method has a problem in that as the size of the semiconductor device increases, the stress which develops between the semiconductor device material and the ceramic multilayer wiring circuit substrate material owing to the temperature change during packaging increases. Accordingly, attempts have been made to bring the thermal expansion coefficient of the ceramic multilayer wiring circuit substrate close to that of the semiconductor device. However, to obtain a high density wiring by using gold, copper, silver etc., which have a low electric resistance, as the wiring conductor material, the thermal expansion coefficient of the ceramic insulating material should be brought close to that of these conductor materials. Thus, the thermal expansion coefficient of the ceramic insulating material is required to be close to that of the semiconductor device material and that of the conductor material. However, no due consideration has been given to a packaging technology suitable under these mutually contradictory conditions.
In a ceramic multilayer circuit substrate, the insulating material is required to have as low a dielectric constant as possible to attain a higher signal propagation speed. Further, the conductor material used is required to have a low electric resistance. As described, for example, in "ceramic multilayer wiring circuit board" [Japanese Patent Application Kokai (Laid-open) No. 11,700/84], a substrate material having a specific dielectric constant of 4 to 5 has been obtained which comprises silica, which has a low dielectric constant, bonded with glass. Further, since the material can be fired at a temperature not higher than 1,000.degree. C., conductor materials of low electric resistance, namely gold, copper, silver etc., can be used in combination therewith. Further, the thermal expansion coefficient of the ceramic multilayer circuit board material has been brought as close to that of the semiconductor device as possible, and is much different from that of the conductor material. Thus, no due attention has been paid to attaining a high density wiring of the internal circuit and yet mounting the semiconductor devices in a high density and with good reliability.
The object of this invention is to provide a packaging technology which gives a ceramic multilayer circuit substrate comprising a ceramic insulating material of lower specific dielectric constant and such conductor material of low resistance as gold, copper, or silver wired in a high density thereon and which makes it possible to mount the semiconductor devices in a high density and with good reliability.